The invention relates to the apparatus for the continuous casting of metals, particularly of steel, in curved path, i.e. to the apparatus in which the casting bar which is cast in a substantially vertical direction by means of a curved open-ended mold, is at first moved along a curved path from which it departs in a substantially horizontal direction, passing through a reversible withdrawing and straightening mechanism.
In known apparatus for this kind, casting bar-guiding means are provided over the whole curved path along which the casting bar is moved, and are arranged at least on the extrados and intrados sides of the casting. These casting bar-guiding means may be in form of idle rollers, skids, or the like, and their function is to support the casting bar and to counteract the internal ferrostatical pressure which tends to expand the casting bar and to break out its solidified skin. Notwithstanding the provision of the said casting-bar guiding means, the breaking out of the solidified skin of the casting bar often occurs when the casting bar is being moved along its curved path, generally within a zone extending over 1.5-2.0 meters from the mold outlet. When the skin breaks, the molten metal flowing out of the casting will settle and solidify between the casting bar-guiding means and the casting bar, thus forming the so-called drippings which prevent any further withdrawal of the casting bar. Therefore, the cleaning and restoring of the casting path which has been effected by the drippings, must be carried out at the end of the casting operation, which will be however continued with the other casting path or paths of the apparatus. Of course, this involves a longer overall casting time, due to the down times and the hard work to be done between one casting operation and the next.
In order to overcome the said problems, some apparatus have been proposed for the continuous casting of metals in curved path. These apparatus are above all intended for the casting of metal casting bars having small sectional dimensions, such as for example a square section up to 140-150 mm each side. The apparatus are fully devoid of means for guiding the casting in the initial section of its curved path below the mold, more particularly over a distance from at least 1.5-2.0 meters from the cold. Thus the advantage is attained of more easily cleaning and restoring the casting path should the skin of the casting bar break. In fact, since the casting bar is not clamped between the casting bar-guiding means along the initial section of its curved path, the casting operation can be easily resumed on the same casting path by reinserting the starter bar or by using as a starter bar the already cast strand. It is thus possible to attain a higher plant utilization factor and to reduce the down time due to the breaking of the metal casting skin.
Problems arise however, with the elimination of the casting bar-guiding means in the region below the mold since the flexible starter bar is not guided and supported in the last portion of its path. In fact, when a flexible or articulated starter bar is not suitably guided, for example on the extrados side, along the curved path below the mold, as well as during its withdrawal from the mold in the initial stage of the casting operation, this starter bar might become stretched along the chord of the arc described by the curved free path, thus determining an uneven pull and breakage of the casting bar at the outlet of the mold.
To solve the problem of the starter bar to be used in the apparatus for the continuous casting of metals in curved path, in which at least one initial portion, starting from the mold, of the casting bar curved path is devoid of casting bar-guiding means, entirely rigid, curved starter bars have been proposed, with a shape conforming to the casting bar curved path, and of a length corresponding to the length or the arc representing the curved path from the mold outlet to the powered extractor roller pair at the outlet of the withdrawing and straightening mechanism. Obviously, these curved rigid starter bars need not to be guided and supported when they are inserted from below into the mold by the same withdrawing and straightening mechanism. They however have the following disadvantages owing to the distance, which might be rather great, between the withdrawing and straightening mechanism on the one hand, and the mold on the other hand. The starter bar, even if it is of the rigid type, might be subjected to elastic strains and/or movements that hinder the insertion of the starter bar head end from below into the mold outlet. Further the construction of the withdrawing and straightening mechanism, that has the task of taking away and moving into its rest or storage position the curved rigid starter bar, as well as the task of withdrawing the casting bar, and of straightening and delivering same in a substantially horizontal direction, then becomes rather complicated and expensive. Moreover, the entirely rigid, curved starter bar takes up a rather important space when it is removed to its rest or storage position, and auxiliary mechanisms are generally required for bringing and maintaining same in its storage position, and for taking it back to its active position.
The invention aims overcome the afore-disclosed problems by providing an apparatus for the continuous casting of metals, particularly of steel, in curved path, in which an initial portion of the casting bar curved path, immediately below the mold and within the spray-cooling chamber, is devoid of casting bar-guiding means. With the apparatus of the invention, notwithstanding the absence of casting bar-guiding means in said initial portion, it is possible to easily and accurately insert the starter bar into, and withdraw the starter bar from the mold, without any tendency of the starter bar to become stretched along the chord of the curved path, and at the same time without significant difficulties and complications in the construction of the withdrawing and straightening mechanism and the storage means.
According to the invention, the casting bar-guiding means that are provided in the last portion of the casting bar curved path, upstream of the withdrawing and straightening mechanism, comprise at least one pair of powered pulling rollers arranged at, or near to their upper end turned towards the mold, while a rigid and curved starter bar is associated to the apparatus. This starter bar substantially has the same curvature as the casting bar curved path, and such a length that when it is positioned to close the mold bottom outlet, it is still engaged between the first pair of powered pulling rollers in the said casting bar-guiding means provided in the last portion of the casting bar curved path, upstream of the withdrawing and straightening mechanism. Thus, by means of the said first pair of powered pulling rollers and of other successive pairs of powered pulling rollers which might be included in the said casting bar-guiding means, and/or in the withdrawing and straightening mechanism, the starter bar can be moved forward up to being engaged between the powered extractor roller pair at the outlet of the withdrawing and straightening mechanism.
The main advantage afforded by the invention resides in the fact that it is possible to use a curved rigid starter bar much shorter than the starter bars which have been used up to now in the apparatus for the continuous casting of metals in curved path, with no casting bar-guiding means in an initial portion below the mold of the casting bar curved path.
In the last portion of the casting bar curved path, between the first pair of powered pulling rollers of the casting bar-guiding means and the last pair of powered pulling or extractor rollers of the withdrawing and straightening mechanism, there might be provided one or more further pairs of powered pulling rollers. The spacing between the several successive pairs of powered pulling rollers forming part of the casting bar-guiding means provided in the last portion of its curved path, and/or of the following withdrawing and straightening mechanism, including the pair of powered extractor rollers at the outlet of said withdrawing and straightening mechanism, does not exceed the length of the starter bar, so that the starter bar is always engaged by at least one pair of powered pulling rollers. The length of the curved rigid starter bar therefore is substantially equal to the distance between the lower mold outlet and the first powered roller pair of the casting bar-guiding means in the last portion of the casting bar curved path, or to the smallest distance between two successive pairs of powered pulling rollers forming part of the said casting bar-guiding means and/or of the withdrawing and straightening mechanism.
In one preferred embodiment of the invention, the casting bar-guiding means are provided only in correspondence with the second half of the casting bar curved path, and the first pair of powered pulling rollers is located at the upper or mold-facing end of said means at a position substantially midway of the arc described by the casting bar curved path, between the mold and the withdrawing and straightening mechanism. In this case, the length of the starter bar is substantially equal to the half of the casting bar curved path from the mold to the withdrawing and straightening mechanism.
The curved, rigid, short starter bar according to the invention may be made of any suitable material, such as for example steel, aluminium, or a light alloy.
The powered pulling roller pair or pairs provided according to the invention in the casting bar-guiding means situated in the last portion of the casting bar curved path, may be operated in any desired manner, for example through a suitable drive taking its power from the withdrawing and straightening mechanism, or else by means of one or more special motors which are synchronized with the motor for driving the said mechanism. Moreover, the two powered pulling rollers in each one of the said roller pairs may be mounted in such a manner that they can be drawn away from, and near to each other, substantially in the radial direction of the casting bar curved path, whereby they are drawn near to each other in order to apply on the starter bar a sufficient pressure for a good and safe grip of the casting bar, while they are drawn away from each other in order to reduce the pressure on the only partly solidified casting bar, so as to avoid any crushing of same.
Apart from the above disclosed features, the casting bar-guiding means provided in the last portion of the casting bar curved path may be constructed in any desired manner, and may comprise idle rollers and/or skids and/or sliding shoes at the intrados and/or at the extrados. It might be even sufficient to have only two casting bar guiding rollers respectively mounted on the intrados, and the extrados side of the casting bar curved path in a facingly arranged relation, downstream of, and preferably the nearest possible to the first powered pulling roller pair.
According to one preferred embodiment of the invention, when all the pairs of superposed rollers in the withdrawing and straightening mechanism or at least those pairs situated in the last section of said mechanism, are of the openable type and constructed in such a manner that the superposed rollers belonging to the same roller pair can be drawn away from each other, the starter bar can be moved into its rest or storage position at least partly in the area of the withdrawing and straightening mechanism, whereby the space taken up by the continuous casting apparatus is considerably reduced, both in length and in height. More particularly, the rollers of all the openable roller pairs of the withdrawing and straightening mechanism, or at least the rollers of the openable roller pairs provided in the last section thereof and possibly only the rollers of the last pair of openable, powered extractor rollers of said withdrawing and straightening mechanism are supported on cantilever means. The structure for supporting the starter bar in its storage position is then provided alongside the path of removal of the starter bar, on the free side of the cantilever rollers. With such an arrangement, the starter bar will be disengaged from the rollers of the said openable roller pairs, by drawing these rollers away from each other, and will be pushed from the side outwardly of the casting path into its storage position on the starter bar supporting structure, while it will be engaged between said openable roller pairs when it is pushed inwardly from the side, in readiness for being inserted into the mold outlet.